Method and device for measuring blood gas parameters

ABSTRACT

The invention relates to a method and device for measuring blood gas parameters, preferably pH, pCO 2 , and pO 2 , in a blood sample, where the blood sample of a patient is fed into at least one measuring cell of an analyzer. In order to obtain accurate values for the blood gas parameters even in cases where the temperature of the patient deviates from normal temperature, the temperature of the patient or blood sample is measured upon sample withdrawal, and the measured temperature is transmitted to the analyzer or is recorded by the analyzer, and the temperature of the measuring cell of the analyzer is adjusted to the measured temperature by cooling or heating.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method and device for measuring bloodgas parameters, preferably pH, pCO₂, and pO₂, in a blood sample, wherethe blood sample of a patient is fed into at least one measuring cell ofan analyzer.

[0002] In the blood gas multi-analyzers described in the literature andcommercially available the measuring cells are thermo-stabilized at bodytemperature, i.e., at 37.0° C. Besides measuring the blood gasparameters pH, pCO₂ and pO₂, these analyzers are used to measureelectrolytes, metabolic parameters and Hb-derivatives. For this reasonthe maximum operating temperature of such analyzers should always besomewhat lower than the temperature of the measuring cell and liesbetween 31° C. and 33° C. in commercially available devices.

DESCRIPTION OF PRIOR ART

[0003] In U.S. Pat. No. 4,548,259 A a measuring cell is described in thecontext of a chemical analyzer for photometric measurement of a liquidsample, which is thermostabilized by being provided on opposing wallswith thermoelements, e.g., Peltier elements, the side walls of themeasuring cell furthermore being provided with temperature sensors formeasuring the cell temperature. After a sample has been fed into themeasuring cell, the cell may be heated or cooled by means of the Peltierelements—depending on the output signal of the temperature sensors—untila predetermined working temperature in the range of 37° C.±0.2° C. isattained. The device described is suitable for the photometricmeasurement of blood samples, for instance, during which temperaturemust be kept constant.

[0004] From DE 26 51 356 A1 a measuring device for the photometry ofliquid samples is known, in which a Peltier element is proposed as aheat-source or heat-sink for the thermo-stabilization of small measuringvessels (and thus small measurement samples). This permits rapid andhighly accurate adjustment of the working temperature (preferably 30°C.) of the measuring device.

[0005] Finally, a blood gas analyzer is described in U.S. Pat. No.4,717,548, which determines blood gas parameters, such as pH, pCO₂, pO₂and temperature, in an extracorporeal blood flow situation, for instanceduring open-heart surgery, and which records the individual signals inreal time. The signals are used for parameter monitoring and mayactivate alarm and switching functions when preset values are exceeded.

[0006] If conventional blood gas multi-analyzers are used for blood gasanalysis with patients whose body temperature deviates from the normaltemperature (37° C.), for instance in special surgery cases during whichbody temperature is artificially lowered, it is standard practice tocorrect the values for pH, pCO₂ and pO₂ obtained from the measuringdevice with the use of mathematical models, in order to find themedically relevant values at the actual body temperature of the patient.Such corrections are rather imprecise, however, and errors of up to 50%may occur.

SUMMARY OF THE INVENTION

[0007] It is the object of the present invention to propose a method formeasuring blood gas parameters, preferably pH, pCO₂ and pO₂, of a bloodsample, and an analyzing device for application of the method, whichpermits the determining of accurate values for the blood gas parameterseven in cases where the temperature of the patient deviates from normaltemperature.

[0008] This object is achieved by the invention by providing that thetemperature of the patient or blood sample is measured upon samplewithdrawal, and that the measured temperature is transmitted to theanalyzer or recorded by the analyzer, and that for measuring blood gasparameters the measuring cell of the analyzer is adjusted to themeasured temperature by heating or cooling.

[0009] The advantage of the method according to the invention lies inthe fact that the partial pressures (pCO₂, pO₂) and the pH-value aremeasured at the actual temperature of the patient, thus giving valueswhich are of immediate physiological relevance, and renderingsuperfluous any error-prone subsequent mathematical correction of themeasured values. The values obtained permit rapid medical action andprovide a basis for emergency measures.

[0010] An analyzing device implementing the method of the invention ischaracterized by a regulating and control unit, which permits regulatingthe temperature of the measuring cell in the range from 22° C. to 40° C.depending on the temperature of the blood or the patient measured at thetime of sampling.

[0011] The method according to the invention will permit a stabletemperature regimen for the measuring cell even at operating or ambienttemperatures which are higher than the temperature of the measuringcell.

[0012] It is of particular advantage if the measuring cell is cooled orheated to the measured temperature before the blood sample is enteredinto the analyzer and if sample entry is enabled only after thistemperature is reached. During an operation the anesthetist or internistis assisted by this arrangement since the analyzer will automaticallysignal when sample entry may take place from the point of view ofmeasurement accuracy.

[0013] In the most basic variant of the invention the blood temperatureor the temperature of the patient may be measured in the conventionalway by means of a thermometer or measuring probe and entered manuallyinto the analyzer via an entry device (keyboard or touchscreen).Measurement of the temperature, data entry into the analyzer, withdrawalof the blood sample and sample entry into the analyzer should all beeffected within a time period of a few minutes, preferably.

[0014] It is of particular advantage if the process is automated in sucha way that the blood or patient temperature is measured by a temperatureprobe placed inside or on the patient, and that the temperature data aretransmitted automatically to the analyzer. In this case a specialadvantage is obtained by continually adjusting the temperature of themeasuring cell synchronously with the actual temperature measured. Forthis purpose the patient temperature may be measured on various parts ofthe body by means of thermometers, temperature sensors or infraredmeasuring cells. For accurately determining the basal temperature theplacing of a sensor in the anal region is indicated.

[0015] It is of advantage if the measurement signal is amplifieddirectly in the measuring probe, and is converted in an A/D-converter,and is transmitted noise-free over a distance of a few meters to theanalyzer interface as an IF or RF signal. Transmission via cable wouldalso be possible.

DETAILED DESCRIPTION OF THE DRAWING

[0016] The invention will be further described below, with reference tothe schematic representation in FIG. 1.

[0017] Reference numeral 1 denotes an analyzer for the measurement ofblood gas parameters, preferably pH, pCO₂ and pO₂, in a blood sample,where the analyzer 1 has at least one thermostabilized measuring cell 2with electrochemical measurement electrodes E, for instance flowsensors. The measuring cell 2 and measurement electrodes E,respectively, can be heated or cooled, for instance by means of Peltierelements 3, via a distributor element 9, which is a good heat conductor,depending on the output signal of a regulating and control device 4,which is connected to a temperature probe 5 placed in or on the patientP. The current temperature of the measuring cell 2, through which asample capillary 10 runs and which is provided with thermal insulation11, is recorded by a temperature sensor 12 whose measurement signal isfed to the regulating unit 4.

[0018] For data transmission to the regulating and control device 4 acable 6 (dashed line) or a wireless link 7 is provided. Depending on thepatient temperature measured by the temperature probe 5 the temperatureof the measuring cell 2 can be regulated over a range of 22° C. to 40°C., the temperature of the measuring cell 2 preferably being continuallyand synchronously adjusted to the currently measured temperature of thepatient P.

[0019] The patient temperature determined by measurement probe 5 mayalso be read off and entered into the analyzer 1 by means of an inputdevice 8, for instance a keyboard.

[0020] Furthermore the analyzer 1 may be provided with a locking device13 on the sample input element, which is controlled by the regulatingand control device 4 and enables sample input only when the temperatureof the measuring cell 2 is equal to the blood or patient temperaturemeasured.

What is claimed is:
 1. A method for measuring blood gas parameters, in ablood sample, comprising the steps of: measuring the temperature of apatient or the temperature of the blood sample upon sample withdrawal,feeding the blood sample of the patient into at least one measuring cellof an analyzer, transmitting the measured temperature to the analyzer,and for measuring said blood gas parameters adjusting the at least onemeasuring cell of the analyzer to the measured temperature by heating orcooling said measuring cell.
 2. A method according to claim 1, whereinthe measuring cell is cooled or heated to the measured temperaturebefore the blood sample is entered into the analyzer, and wherein sampleentry is enabled only after said measured temperature is reached.
 3. Amethod according to claim 1, wherein the blood or patient temperature ismeasured by a temperature probe placed in or on the patient and thetemperature data are transmitted automatically to the analyzer.
 4. Amethod according to claim 1, wherein the temperature of the measuringcell is continually adjusted synchronously with the actual temperaturemeasured.
 5. A method according to claim 1, wherein the temperature ofthe measuring cell of the analyzer is regulated in a range from 22° C.to 40° C., depending on the temperature measured.
 6. A method accordingto claim 5, wherein the transmission of the measured temperature to theanalyzer is performed via cable, via IF signal, or via RF signal.
 7. Amethod according to claim 1, wherein at least one blood gas parameter ofa group consisting of pH, pCO₂, and pO₂ is measured.
 8. An analyzer formeasuring blood gas parameters in a blood sample, with at least onethermostabilized measuring cell, wherein a regulating and control unitis provided, which permits the temperature of the measuring cell to beregulated in a range from 22° C. to 40° C., depending on blood sampletemperature or a patient temperature measured upon sample withdrawal. 9.An analyzer according to claim 8, wherein the analyzer is provided witha locking device on a sample input element, which is controlled by theregulating and control device and enables sample input only whenmeasuring cell temperature is equal to the blood sample temperature orpatient temperature measured.
 10. An analyzer according to claim 8,wherein the regulating and control unit is connected to a temperatureprobe placed in or on the patient, and wherein a cable or wireless linkis provided for data transmission to the regulating and control unit.